Radio direction finder



Oct, 31, 1944. P. B. TAYLOR RADIO DIRECTION FINDER Filled Noi. 18. 19372 Sheets-Sheet 1 DIRECT/0N /r/IVQE@ Recall/GR Illl l ,r Il

Oct. 31, 1944.

P. B. TAYLOR RADIO DIRECTION FINDER Filed NOV. 18, 1937 A /POL E 2Sheets-Sheet 2 @EN a irre/Quay:

Patented Oei. 31, 1944 ETED STTES OFFICE (Granted under the act of March3, 1883, as i amended April 30, 1928; 370 0. G. 757) 19 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to radio direction finders and proposes a systemin which the principle of phase relationship of spaced loop antenas isemployed to obtain a directional indication of a source ofelectromagnetic wave enelgy.

It is well known that the common loop antenna is inaccurate as adirection finder when the received wave or beam makes an angle to thehorizontal, the error being generally known as night eliect, It is animportant object of the present invention to overcome night effect.

Another important object of the invention is to provide means wherebyvery small loop separations are possible, thus making the apparatus morecompact.`

It is also an object of the invention to give accurate indication and todenne one true course without ninety degree or one hundred and eightydegrees ambiguity. Other objects will aJppear as the descriptionproceeds.

The invention will be described with reference to the accompanyingdrawings, in which:

Fig. 1 shows an embodiment of the invention in which the loops areconnected in parallel;

Fig. 2 illustrates an embodilment in which the loops are shown connectedin series;

Fig. 3 shows a modified form in which the spaced identical loops areemployed with a separate reference loop.

Fig. 4 is a vector diagram depicting the phase relationships between thevoltages e' and e induced separately in the two loops, and theireffective resultant E. M. F. expressed by 2 sin /2;

Fig, 5 shows another embodiment of the invention in which spaced loopsare employed with a separatel reference antenna of the vertical type;and

Fig. 6 illustrates diagrammatically the functioning of a cathode raytube indicator employed as in Fig. 3.

One form of direction nder system which s largely free from night effecterror is known as the Adcock antenna system. Another form oi system alsofree from night effect error embodies an arrangement of spaced loops.The spaced loop direction finder may be regarded as an Adcock systemwhere loops are substituted for vertical antennas, and the theory ofoperation is similar, being based on the diierence of phase of thesignals in the two loops, which is due to the difference of time ofarrival of the received signal at the two separated loops.

The present invention comprises an arrangement of identical separatedloop antennas, the planes of the loops being perpendicular to a commonaxis passing through their centers.V

d=separation between loops L=wave length of received signal 0=ang1ebetween ray and the plane of the loops.

If the loops are oriented so that the ray lies in the loop plane, thephase diierence is zero. If then the signals froml the two loops arecombined differentially, being equal in magnitude and opposite in phase,their resultant should be zero. For any other direction of the ray therewill be a difference of phase and the resultant will not be zero (exceptwhen the separate signais vanish). It is the vanishing of the resultantsignal which is used to locate the direction of arrival of the wave. Ii'the loops are vertical the bearing sought will be the horizontal linethrough the plane of the loops.

In the prior art pertaining to systems in which spaced loops areemployed, separation of the loops has been large-of the order of a halfwave length. For the purpose of mounting in any restricted space orposition, as, for instance, on an airplane, it is desirable that theseparation be greatly reduced. Another advantage of small separationlies in the increased freedom from diversity effect, that is, the effectof irregularities of phase, polarization and intensity between widelyseparated points due to inhomogeneity of the radio waves. If theseparation of the spaced loops be reduced, however, the diierence inphase between the signal outputs becomes very small, even when theincoming wave is at a considerable angle to the plane of the loops, andthe difference of phase due to unequal tuning of the two loops or toother differences between the two pickup circuits becomes greater thanthe difference in phase which is to be detected. For instance,

with a loop separation of one meter, a Wave length of 50 meters and anangular displacement of the ray or beam from the loop plane of degreesthe phase dierence between the signals is only 38 minutes and theresultant dilerential signal is reduced to only .05 of the signal to beobtained from one of the, loops separately.

In the present invention a short separation is made practicable bycombining the-two signal pick-up circuits in such a manner that the verysmall diiierences of phase between the component signals are preservedcorrectly and obscuring eiects are prevented.

It is well known in electrical theory that the degree of connectionbetween two parts of a circuit may be varied according to the nature ofthe intervening circuit elements. This variable degree of coupling ismost commonly recognized in transformer coupling, but existsior allcir-- cuits of whatever nature. In general, it may be said that as thecoupling approaches 100 per cent the possibility rof phase'displacementbetween the two signals due to mistuningof any part of the circuit isdiminished. This is because the multiple resonance frequencies of amultiple branched circuit are thereby reduced to a single frequency. Inpractice the tightest coupling between the parts of a circuit is usuallyobtained by pure conductive coupling, but at high frequencies this maybe dicult tov effect due to stray reactances.

In the present invention phase error is therefore minimized by combiningthe pick-up circuits of the loops in a network in which the impedance ofthe circuit in which the pick-up voltages act in series vis minimizedand/or the impedance of circuits in which the pick-up voltages act inparallel or separately is maximized. This type of network at the sametime operates to minimize any unwanted pick-up arising by virtue ofstraycoupling of parts of the circuit to surrounding objects. This typeof network is tuned .by a single tuning element which is best insertedin the series circuit ifv its impedance is low andl across the parallelcircuit if its impedance is high.

These considerations regarding'the connecting network apply no matterwhat type Aof pick-up f is employed, whether loops or dipoles, but loopcircuits are more easily shielded and controlled than dipoles.

In the present invention, means has been devised whereby the two signalsare combined in such a manner that the very small diierences ofk phasebetween the component signals are preserved, so that very small loopseparations are possible, thus making the physical apparatus much morecompact.

Referring to embodiments of the invention shown in Figs. 1 and 2,numeralsv I and 2 designate an arrangement of similar loop antennas, twoloops being here shown by way of example, with their centers as at 3 andll. These loops are spaced from one 'another and the distance betweentheir centers may be denoted by the letter d. As here shown, the loops Iand 2 are perpendicular to the line S-l. As shown in Fig. 1, the loopsare connected in parallel circuit tocommon terminals 5 and E. A commontuning condenser as 9 is connected across theleads as shown. The leadsof loop 2 are shown reversed so that when like voltages e' `and e" areinduced in both loops the output is zero. An electro-static shield isshown surrounding the loops and their connecting leads. The terminals 5and 6 lead to a radio lll receiver as at l, which may be a conventionalreceiver, or any one of the types oi receiver especially designed forradio direction finding and employing the principle of right and leftindication. This receiver, it may be noted,` presents to the two loops acommon terminating impedance and a common detector.

The present invention in its nature and scope comprehends the idea ofjoining two similar l spaced loops in a circuit of low series impedance,differentially and with a common tuning unit and output terminalssymmetrically situated between f loops as shown in said figure.

the loops. When such a circuit is acted upon by a plane wave radiosignal, no voltage can appear across the output terminals except thatdue to a difference in phase of the signals inducedin the two loops. thereceiver may be comparatively weak due to the short separationn betweenthe loops and the consequent slight difference of phase, at the sametime all static and interfering noises are also greatly reduced and itis possible to operate the receiver down to the level of tube noise.

If e be regarded as the amplitude of the E. M. F. induced in each loopseparately and p the phase difference, the net effective induced E. M.F. may be shown to be of amplitude 2c sin 1a/2 (see Fig. 4)

In the form of the invention as shown in Figure 2, where the spacedloops I and 2 are shown connected in series with the common dividedtuning condensers I and I I, an advantage is secured in that the outputof the spaced loop is less affected in phase by small differences inimpedance between the two component loops.

In th'e modication shown in Fig. 3, a loop fixed rigidly and in parallelrelation .to the spaced loops is employed as a reference antenna, and islocated preferably midway .between said main One advantage of thisarrangement lies in the fact that in any system using aright-leitindicator, the indications are much steadier both on andoicourse due to the fact that fading is less severe with loop reception,that intensity of signal reception is not aiected by change of angle ofincidence of the received ray or beam, also for the reason that bettershielding can be secured and that the fore-aft signal directionambiguity may yIoe resolved.

It should be understood that spaced loops as employed in the presentinventionmay be combined with a vertical antenna to operate as adirection finder' which-will also be free from night effect error.

One example of an arrangement by which this may. be done is shown inFig.l5. I and 2 are spaced loops, which constitute a directionalreceiving antenna. Numeral 22 designates a Vertical doublet, whichconstitutes the antenna for reference signal. As collector for referencesignal any type of antenna may be used thaty does not change phaseofoutput as ther direction of the received ray changes from one side tothe other of the plane of lthe loops. An audio signal generated inoscillator *I Siy is applied in modulator i8 to the reference signalfrom 22 modulating or commutating it. Loop' signal from I and 2 issuperposed upon the'modulated reference signal in suitable phaserelation in combining circuit il is then amplied and detected inreceiver 20 and the output combined with signal direct from oscillatorI9 in indicator 2| to give right-left in- Thus, while the-signaldelivered into dication of the bearing of the received radio signal.

With this arrangement when the signal fades or changes its angle ofpolarization the intensity of the induced E. M. F, in the directionalspaced loops and in the reference loop change together preserving aconstant ratio of voltage to each other. Thus, by applying AVCcontrolled by the reference loop to both signals, fluctuations ofindication from the above causes may be eliminated.

The ratio of induced voltage in the double loop to that in the singleloop is where A'is a factor which may be made a Vconstant of theequipment.

By then applying methods which eifectivell7 make use of this ratio, itis possible to measure and indicate the angle and through it angle 0. Solong as the angle which the received wave makes with the horizontal issmall, is substan- 'tially equal to the off-null bearing of the signal.

The modification as shown in Fig. 3 where spaced loops are used incombination with a reference loop, may employ a cathode ray tube toindicate bearing. Referring to said Fig.y 3, signals from the spacedloops I and 2 and from the reference loop I2 are amplified in separatereceivers I3 and I4, the degree of amplification being greater in theamplifier I3 fed from the spaced loops I and 2 than in amplifier I5 fedfrom the reference loop I2, said difference being in the ratio Bil/21rd,where B is a constant of the apparatus. If now the outputs are appliedrespectively to the crossed plates of the cathode ray tube shown at `IBand properly phased by means of a phase shifter shown as at I4, a:straight line pattern will be seen, which can be made vertical, say for0:0 (on-course bearing) `and which for any given value of qi will turnfrom the vertical an angle ,b such that tan =K sin 0 of spaced loops androtating with the same provides for the elimination of 90 and 180arnbiguity.

The functioning of a cathode ray tube when used as an indicatol` may bevisualized by reference to Fig. 6. The component motions of the luminousspot are shown as proportional to the amplified reference signal andspaced loop Signal respectively, the amplifications being such as tomake the factor K equal 2 in the diagram. The resultant line traced bythe motion of the spot is shown making an angle ip with the axis of thereference signal vector. Corresponding to various angles 1]/ there aremarked on the circumference about the tube the angles 0, which are thedirections of signal bearing referred to the plane of the spaced loops.

Changes, modifications and equivalent arrangements are contemplatedwithin the scope and spirit of the invention as defined by the appendedclaims.

I claim:

1. In a radio direction finder, an antenna system comprising spacedloops having their planes 'perpendicular to their common line ofcenters; a circuit for conductively and differentially coujpling saidloops in operative relation, and including a common tuning element and acommon terminating impedance in said circuit.

2. In a radio' direction finder, a directional antenna system comprisingspaced parallel loops having their planes perpendicular to their commonline of centers; a circuit for operatively coupliiig said loopsconductively and in opposition; a. common tuning means in said circuit;an output circuit connected in parallel-to said firstnamed circuit; andmeans in said output circuit for comparing and indicating relative phasedis- 1 placement between the outputs of said loops.

3. In a radio direction finder, an antenna system comprising spacedparallel loops having their planes perpendicular to their common line ofcenters; a commony output Vcircuit couplingV said loops in series, and acommon tuning element in said circuit; and means fed from said outputcircuit for comparing and indicating relative phase displacementsbetween the outputs of said loops.

4. In a direction finder, a directional antenna system comprising a pairof loops spaced from one another and having their planes perpendicularto their common line of centers; a circuit conductively anddifferentially coupling said loops; a common tuning element in saidcircuit; a common output circuit for said loops and means in saidcircuit including a receiver for indicating a bearing dependent uponrelative phase displacements between the output of said loops.

5. In a radio directional antenna array, a system comprising two spacedloops having their planes perpendicular to their common line of centers;a circuit for closely and diierentially coupling said loops in operativerelation, and including a common tuning element in said circuit.

6. In a radio directional receiver, an antenna system comprising spacedloops having their planes perpendicular to their common line of centers;a circuit for conductively and differentially coupling said loops inoperative relation; common tuning means in said circuit; and a commonreceiver into which the combined signal output of the loops is fed.

7. In a radio direction nder, a pair of parallel loops spaced from oneanother and having their planes perpendicular to their common line ofcenters; a circuit system for operatively coupling said loopsconductively and in opposing circuit relation, said circuit includingtuning means common to said loops; a: separate reference loop spaced inparallelism with said first-named loops, and phase shifting means fedfrom said reference loop; an amplifier for the energy output of thespaced loops; an amplifier for the energy output of said reference loop;and means responsive to the outputs of said amplifiers to indicate thebearing of a signal 4dependent upon the phase displacement between thesignals picked up by said spaced loops.

8. In a. radio direction finder, a pair of parallel loops spaced fromone another and having their planes perpendicular to their common lineof centers; a circuit system for conductively and differentiallycoupling said loops, said circuit including a common tuning meansconnected in the common output of said loops; an auxiliary referenceloop interposed in spaced parallel relation between said first-namedloops; an amplifier for the signal output of said coacting spaced loops;a phase shifter fed from said reference loop; an amplifier coupled tothe shifter for amplifying the signal energy from said reference loop;and

means includingfa ,cathode Aray, tubeactuatedby signals from saidamplifiers togive anindication of I.bearing iny response to phasedisplacementslas determined by said, mst-.named .Spacedloopsj 9..v In;a.,radio. .directional ,syste1 n, a, directional, antenna array.comprising al p air of. loops spaced from-one. another, havingtheirplanes VVVperpen-A dicular to` their common line of .centers ;v acircuitincluding a ,tuned impedancethrough Whichsaid loopsare ,closely ,coupledelectrically in opposing, relation andhaving a` common output signalgareference antenna; means for combining vin, ,suite able phasev theVsignal outputs of the Arespective directional array,` and the .referenceairterma.;4 means for indicating, bearing of. .the` received. raydependent ppon the directionalI ,properties .of r,saiddirectionalantenna array inherent byY virtue., of the. :spacedrelationofsaid. loops. f t

10. In adirection finder thecombination which includes a pair ofdirectional antennas andan auxiliary directional antenna, said antennasbeing rotatably mounted-and havinggSmilar directional characteristics,an indicator having separate .control means for causing a resultantdeiiection,

means forA applying the. output'potentialffrom said auxiliary antenna.to; one; of said-control means, and means for-applyingthe.diilierencelfof the output potentials from said.; pair ofE antennas totheother of Asaid control means. K

11. Inv adirection nder the icombination which includesxa pair `of`directional Iantennas andanauxiliary directional; antenna, saidantennasbeing rotatably ,mounted and. having, similar directional.characteristics, a cathode yray,ind1C 2.ll,or having vertical andhorizontal d,effiacting;l means,- means for-applying the outputpotential-from said .auxiliary antennato; onefof; said deiiecting means,and means for applying the diierencegof the output'ivpotentialsfrom1saidpair. of antennas to the other of said deecting means;l

12. In a direction finder thecombinatiomwhch includes a pair'of'framesantennas andan: auxil.- iary frame antenna.A mounted in.--parallelgplanes and adapted to rotate about. va commonnaxisianindicator having separate` control.. means'. for causing a resultantdeflection, means l.fon appl-yf: ing the output potential of'Said-auXiIiary-.frame antenna to one of said control means,.and.meansiorapplyingtthe difference of` theoutput poten.- tials` from-said pairof framenantennasltothe other of vsaid control-means 13. -Ina directionfinder the combinationiwfhich includes a pair ofdirectionalwantennas-.and';:an auxiliary directional antenna,- said.,antennas t being rotatably mounted and having similar. .dii-

rectional characteristics,` aV pair of i receivers; means for applyingvthe outputlpotentialsfof said pairhof antennas Yin--phase opposition toonefzof said receivers, means-ior applying the loutput potential ofysaid auxiliary antennatdthesot'ner of said receivers, anindicated-meansior, confnecting the output ofvsaidreceiversato saidindi;- cator, and means for adjusting therelative .phase ofnthe outputIpotentials of said receivers..

14.v VI'n-'a direction finderthe combination which includes-- a -pair ofdirectional antennas and` an auxiliarydirectional antenna mounted in;aroW and all oriented inparallel planestohavefsiniilardirectional.characteristics when considered indi,-

vidually; saidantennas being rotatable asaunit about anaxisperpendicularto the,y line. established by saidrow of antennasan indicator hav,.-ingseparate ,controlmeans vfor causing alresultantzdeiiection, means forapplyingvtheoutput assigne potentialirorn said auxiliary antenna tooneot 'said' control means, and 1Vrneans for applying fthe differenceofthe output potentials from ysaidgpijtirofantennas V,tcpthe other of saidcontrol means; 1.5.', `In a direction finder thecombination whichincludes'` a pair of directional y' antennas and" anr auxiliarydirectional antenna mounted in a rowJ and .all oriented in parallelplanes .to have similarv directional,characteristics When consideredinfdividually, said antennas being rotatable as` ay unit aboutl an axisperpendicular to the line established ;bysaid row of antennas., acathode ray indicator having vertical and horizontal deflecting dincludes `fpair off loop antennas and an auxiliary loop antennamountedina row and all oriented.` ingparallel planes to.have similar directionalcharacteristics/ when considered individually, saidallrt tennas beingrotatable as a unit about an axis perpendicular to the line establishedby. said row, of, antennas, an indicator havingseparate` control meansforcausing a 4resultant deection, means for. applying the outputpotential of said auxiliaryv loopantenna to one of said control means,Vand means for applying the difference of the output. potentials fromsaid pair of loop antennastothe other of said control means.

17.- In a direction iinder the combination which.

-includesa-pair of directional antennasandan auxiliary v,directionalantenna, mounted in` arow and allforiented inparallel planes to havesimilar directional characteristics when considered in,

. dividually, said-antennas being rotatable as aunit l means forapplying the output potentials of said 18. In a direction nnder thecombination which includes a pair of loop antennas spacedf and orientedin parallell planes to have similar directional characteristicswhenconsidered individual? ly, an auxiliary loop antennav mounted interme-ldiatethe antennas of said pair and orientedin aplaneparallelto theplanes of* said pair. oflane tennas, said'antennas .being rotatable asAalunit about` an axis perpendicular to the line fbetween said pairofantennas, a cathode rayfindicator havingv vertical and vhorizontaldeflecting means, meansv for applying the output potential lfromsaid-auxiliary loop antenna toene -ofsaid deect; ing-means, and meansyfor applying thedifference-.of the output potentials from said. pair ofloop antennas to the otherv of lsaid deecting means.-

192' In a radio direction nder a pair of spaced parallel similar loopantennas, a third `loop -an. tenna fixed parallel t0 the first pair, anda phase meter responsive to the outputs of the pairedloops compoundedvin opposition and to they outputc of the reference loop.

PAUL B; TAYLOR;

